Method for producing high hydrogen sulfide content gas wells

ABSTRACT

Sulfur precipitation in the production tubing string of wells producing gas with a high hydrogen sulfide content is reduced by circulating a hot fluid down an insulated circulating tubing string and up the casing-production tubing annulus to heat produced fluid in the production tubing string and, simultaneously, injecting a hot oil into produced fluid adjacent the productive interval to dissolve precipitated sulfur and/or otherwise prevent sulfur deposition on the inside of the tubing string as the hot oil mixes with this fluid and is produced up the tubing string.

United States Patent [191 Eickmeier METHOD FOR PRODUCING HIGH HYDROGENSULFIDE CONTENT GAS WELLS [76] Inventor: James R. Eickmeier, 403 309Eighth Ave. S.W., Calgary, Alberta, Canada 22 Filed: June 7,1972

21 Appl. No.: 260,682

[52] US. Cl. 166/303 [51] Int. Cl E211) 43/24 [58] Field of Search166/302, 303, 57; 299/5, 299/6 [56] References Cited UNITED STATESPATENTS 3,415,573 12/1968 Fraser 299/5 X 3,451,479 6/1969 Parker 166/3033,393,733 7/1968 Kuo et al.. 299/5 X 895,612 8/1908 Baker 166/57 [451Mar. 12, 1974 738,326 9/1903 Higgins 166/57 UX 3,531,160 9/1970 Fisher299/5 3,399,623 9/1968 Creed 166/302 UX 3,113,622 12/1963 Carpenter166/302 3,410,347 11/1968 Triplett et al 166/302 X PrimaryExaminerStephen J. Novosad Attorney, Agent, or FirmTom M. Moran [5 7]ABSTRACT 10 Claims, 1 Drawing Figure HOT OIL SOURCE SOURCE SOURCEPAIENIEDm 12 1974 METHOD FOR PRODUCING HIGH HYDROGEN SULFIDE CONTENT GASWELLS BACKGROUND OF THE INVENTION hydrogen sulfide-hydrocarbon fluidflows upwardly through the tubing string the. pressure on the fluiddecreases due to the reduction of the static head in the fluid column.The temperature also tends to decrease. Under these changedpressure-temperature conditions the solubility of elemental sulfurdissolved in the reservoir fluid decreases markedly and sulfur tends tocome out of solution and crystalize on the tubing string causingplugging of the pipe. Plugging by sulfur deposition can become so severeas to cause stoppage of the recovery of fluids from the production well.

It has been suggested, for example see U.S. Pat No. 3,393,733 to C. H.Kuo et al, that such sulfur deposition may be prevented by injecting ahot fluid miscible with the reservoir fluid into the production tubingstring near the productive interval. This injected fluid mixes with hereservoir fluids and the combined fluid is produced up the tubingstring. The injected miscible liquid dissolves sulfur as it forms in thetubing or by other means prevents sulfur-from depositing on the tubing.Injected fluid temperature and rate are determined to satisfy thecondition that injected fluid take into solution, or otherwise transportto the surface, all sulfur which precipitates in the tubing.

This prior art production technique has the disadvantage that injectedfluid, which is generally more dense than produced fluid, is required insuch quantity as to significantly increase the pressure gradient in thetubing string. This imposes an increased back-pressure on the productiveformation and results in decreased well deliverability. In addition, thelarge amount of elemental sulfur contained in the injected fluid must beseparated from that fluid at the surfaceif the sulfur is to be recoveredor if the solvent is to be reused. This may require a substantial amountof separating equipment and attendant expense.

SUMMARY OF THE INVENTION It has now been found that sulfur-containingfluid' can be produced from a subsurface formation without plugging ofthe production tubing from sulfur deposition by flowing the fluid to thesurface through a production tubing string while heating the flowingsulfurcontaining fluid indirectly by heating the production tubingstring and thereby conductively heating the flowing fluid. For example,heat may be supplied to the production tubing string from electricheating coils disposed around the tubing string or by circulating a hotfluid into the well and into contact with the exterior of the productiontubing string. The flowing sulfurcontaining fluid may be concurrentlyheated directly by injecting a hot sulfur-solvent into the well and intocontact with the produced sulfur-containing fluid.

According to a specific embodiment of the method of invention, a wellbore extending from the surface to a formation of interest containing afluid having a high hydrogen sulfide content is at least partially linedwith a large diameter tubular casing and is completed so as to be influid communication with the formation. A first string of tubing, aproduction tubing string, is then extended into the well to a pointadjacent the bottom of the productive formation. The casing-productiontubing string annulus is packed off with a pack-off means set above theproductive formation and a second string of tubing, a hot-oil injectionstring, is extended into the well bore and through the pack-off means toconnect this hot oil injection string in fluidcommunication with thepacked-off interval of the well bore opposite the productive formation.A third string of tubing, an insulated circulating string, is theninstalled in the casingproduction tubing annulus so as to extendthroughout a major length of the annulus above the pack-off means. i

Hydrogen sulfide rich fluid may. than be produced from the productiveformation through the production tubing string. Simultaneously, a hotfluid, such as steam having a temperature about 300 F, is circulateddown the insulated circulating tubing string and up thecasing-production tubing annulus in an amount sufficient to heat theproduced fluid in the production tubing string and thereby maintain thetemperature of this fluid above a pre-detennined minimum temperature,which is preferably above the melting point of sulfur. Concurrently, afluid in which sulfur is soluble, such as a light substantiallysulfur-free crude oil, advantageously can be injected down the injectiontubing string into the packed-off interval of the well bore and producedup the production tubing string with the reservoir fluid in an amountsufficient to dissolve precipitated sulfur, or to otherwise preventsulfur deposition, on the inside of the production tubing string as thehot oil mixes with the produced fluid and is produced up the productiontubing string.

When operating according to this method the amount of sulfur solventinjected down the injection tubing string is substantially reduced incomparison to that used in prior art methods. This reduction is achievedbecause the sulfur carrying capacity of oil and produced fluids isincreased at higher temperatures, because the sulfur which is formed attemperatures above the melting point of sulfur may be of such a naturethat it will not readily plug the production string, and because themethod will result in higher'flowing pressures which will result in lesssulfur formation in the production string.

The method results in higher flowing pressures in the production stringbecause the reduced solvent injection requirement results in lowerdensity fluid flowing in the tubing string. Heat transfer from theannulus into the production tubing also lowers the density of theflowing fluid and contributes to higher flowing pressures.

At these higher flowing pressures, the cooling associated with flashingof well fluids does not necessarily occur in the tubing string since itis possible to flow the well while maintaining minimum tubing flowingpressure above the bubble point pressure of produced fluids. Because ofthe lighter fluid column in the tubing 3 string wells demonstrategreater deliverability and greater ultimate recovery. At the resultinghigher production rates the produced fluids contribute more of the totalheat required to offset well bore heat losses and thereby reduce theamount of heat required to be injected down the circulating tubingstring.

BRIEF DESCRIPTION OF THE DRAWING The Drawing shows a view, partly incross-section, of an earth formation penetrated by a well suitablyequipped for the practice of this invention.

DESCRIPTION OF PREFERRED EMBODIMENT Referring to the drawing, we see asubsurface, fluidcontaining earth formation penetrated by a well 11. Thewell 11 is provided with equipment of a type suitable for the practiceof an embodiment of this invention. The well 11 may be completed in aconventional manner. For example, a casing 12 may be run from thesurface into the well to a point adjacent the bottom of the formation 10and fixed in place with a cement 13. The well bore hole 14 may be openedinto communication with the formation 10 by perforating the casing 12and cement 13 with a number of perforations 15.

t To produce a fluid having a high hydrogen sulfide content from theformation 10 according to this embodiment of the invention, a productiontubing string 16 may be run into the bore hole 14 to a point adjacentthe productive formation 10. The annular space 17 between the productiontubing string 16 and the casing 12 may then be packed off abovethe-productive interval 10 with a suitable pack-off means such as packer18. The packer 18 is preferably of a type adapted for use in duallycompleted wells and is preferably made from materials which areresistant to H 8 corrosion.

A second string of tubing, a hot oil injection string 9, may be extendedinto the well bore and connected in fluid communication with theproduction tubing string 16 at a point sufficiently deep to provide forthe injection of hot oil-solvent into the produced fluid stream beforesulfur precipitation occurs. The connection between the hot oilinjection string 19 and the production string-16 may be made in anysuitable manner. For example, if the packer 18is of the type used indual completions, the hot oil injection string 19 maybe extended throughthe packer 18 thus connecting the hot oil injection string 19 in fluidcommunication with the packedoff interval of the bore hole 14 adjacentthe formation 10 and, through the packed-off interval, into fluidcommunication with the production tubing string 16.

A third tubing string, advantageously, an insulatedcirculating string 20may be installed in the annular space 17 between casing 12 andproduction tubing string 16 throughout a major length of that annulus 17above the packer 18. The circulating string 20 for best results extendsinto the annulus 17 to a sufficient depth such that by circulating hotfluid down the circulating string 20 and p the annulus 17 thetemperature of substantially all produced fluid in the production string16 is maintained above a desired minimum which is advantageously abovethe melting point of sulfur.

The circulating string 20 may be'insulated in any suitable manner. Forexample, the circulating string 20 may comprise two concentric tubingstrings 21 and 22 I with a closed annular space 23 between the strings21 and 22. The annular space 23 may be filled with a low pressure gas orwith other suitable insulating material.

Insulation of circulating tubing string 20 minimizes heat transfer tothe borehole 14 and surrounding earth formations as a heated fluidpasses down the circulating string 20 from the'surface of the earth. Thecirculating tubing string 20 may be connected in fluid communicationwith a source of heated fluid such as steam source 24. This steam source24 is preferably connected in fluid communication with the bore hole 14near the earths surface, as by a conduit 224, so that fluid which flowsdown circulating string 20 may be returned to the steam source byflowing up the annular space 17 and through the conduit 25.

The injection tubing string 19 may be connected at the surface incommunication with a source of a solvent capable of carrying to thesurface elemental sulfur which may tend to precipitate in the productiontubing string 16. For example, the injection tubing string may be incommunication with a source of hot oil 26. The casing 12 is preferablyclosed at the surface with a suitable well head closure assembly 27.

-According to this embodiment of the invention, hydrogen sulfide-richfluid is produced'from the formation 10 through the production tubingstring 16. Simultaneously, a hot fluid such as steam having atemperature about 300 F is circulated from steam source 24 down theinsulated circulating string 20 and up the casing-production tubingannulus 17 in an amount sufficient to heat the produced fluid in theproduction tubing string and, thus, maintain the temperature of thisfluid above a pre-determined minimum temperature which is advantageouslyabove the melting point of sulfur. The total amount of heat required atthe bottom of the circulating string 20 may be determined by consideringheat losses to the equipment in the well 11 and to formations penetratedby the well as fluid moves down the circulating tubing 20 and byconsidering the desired minimum temperature to be maintained in theproduced fluid.

This minimum temperature, which is advantageously in the range of to 250F, is selected to minimize the amount of sulfur coming out of solutionin the well annulus. The required temperature, of course, varies withthe properties of the produced fluid. Important considerations indetermining the desired minimum temperature are that the sulfur carryingcapacity 'ofo il and produced fluids is increased at highertemperatures, and that sulfur formed at temperatures approaching andabove the melting point may be of such a nature that it will not readilyplug the production string. To maintain the desired minimum the annulus17 is advantageously maintained at a minimum temperj ature within therange of about 180 F to about 250 F 7 along its entire length.

To supplement heat circulated down the circulating tubing string 20, asulfur solvent, for example light crude oil of about 35 API gravityheated to a temperature in the range of about 250 to 450 F, may beconcurrently injected down the injection tubing string 19 from hot oilsource 26 and into the packed-off interval of the bore hole 14 adjacentthe formation 10. In many wells the fluid in the formation 10 is aliquid at prevailing conditions of temperature and pressure. The hotoil, therefore, mixes miscibly with this produced fluid and is carriedup the production tubing string 16 along with the reservoir fluid. Asthe mixture of fluids moves up the production tubing string 16, thepressure and temperature of the flowing fluids may be lowered tending tocause sulfur to precipitate. The hot oil dissolves or otherwise carriesto the surface this sulfur which might otherwise be deposited in thewell bore. Therefore, the hot oil is preferably injected down theproduction tubing string 16 in an amount at least sufficient to dissolveprecipitated sulfur or otherwise prevent (as by providing heat to theproduced fluid) sulfur deposition on the inside of the production tubingstring 16 as the hot oil mixes with the produced fluid and is producedup the production tubing string 16. However, in order to reduce theincreased fluid pressure gradient in the production tubing string 16caused by the relatively high density hot oil, the amount of hot oilinjected should be as low as possible to achieve the desired results. inmany wells, injection of hot oil may not be necessary since sufficientheat to prevent sulfur deposition in the production tubing string 16 maybe supplied through the circulating tubing string 20.

By reducing injection of hot oil and by heating fluid in the productiontubing string 16, operating according to the present invention providesa produced fluid column lighter than that obtained in prior artproduction methods. This results in higher flowing pressures in thetubing 16. At such higher flowing'pressures the considerable coolingassociated with the flashing of produced fluid from the liquid to thegas phase may not occur in the tubing string 16. It may be possible toflow the well 11 while maintaining minimum flowing pressure throughoutthe production tubing string 16 above the bubble point pressure of thereservoir fluid. This significantly reduces the precipitation of sulfurin the well 11. Additionally, the well 11 may demonstrate greaterdeliverability and greater ultimate flowing recovery as a result of thelighter fluid column in the tubing string. Also, injected heatrequirements are reduced since reservoir fluids are produced morerapidly and therefore lose less heat to the well 11.

The embodiment of the invention in which an exclusive property orprevilege is claimed are defined as follows:

1. A method for preventing sulfur deposition in the production tubingstring of a well producing a sulfurcontaining fluid from a subterraneanearth formation which comprises:

flowing the sulfur-containing fluid from the earth formation to thesurface through the production tubing string; and

simultaneously heating the production tubing string by circulating aheated fluid into the well through an insulated string of pipe and upthe casingproduction tubing annulus to thereby indirectly heat theflowing sulfur-containing fluid in the production tubing string. v

2. The method of claim 1 where the hot fluid is steam.

3. The method of claim 1 where the heated fluid has a temperaturesufficient to maintain the temperature of the flowing sulfur-containingfluid above the melting point of sulfur.

4. The method of claim 1 including the step of injecting a hotsulfur-solvent into the flowing sulfurcontaining fluid through aninjection tubing string connected in fluid communication with theproduction tubing string at a point below a pack-off means in the saidwell.

5. The method of claim 4 where the hot sulfursolvent is a heated lightcrude oil.

6. The method of claim 4 wherein the hot sulfursolvent is heated to atemperature in the range of 250 to 450 F.

7. A method of producing a fluid having a high hydrogen sulfide contentfrom a fluid-containing subsurface earth formation through wells withoutplugging the wells with sulfur precipitate which comprises the steps of:

providing a well bore extending from the earth surface to the subsurfaceearth formation;

lining at least a part of the well bore with a tubular casing;completing the well bore in fluid communication with the subsurfaceearth formation;

extending a production tubing string into the wellbore to a pointadajacent the subsurface earth formation whereby an annulus is definedbetween the tubular casing and the production string of tubing;

packing off the annulus with a pack off means set at a point in the wellbore above the subsurface earth formation to prevent fluid flow up theannulus from the subsurface earth formation; extending an insulatedcirculating tubing string into the annulus to a point above the pack offmeans;

producing fluid having a high hydrogen sulfide content up the productiontubing string from the subsurface earth formation;

and simultaneously circulating a hot fluid down the insulatedcirculating string and up the annulus to heat the produced fluid in theproduction tubing string and thereby retard sulfur precipitation in theproduction tubing string 8. The method of claim 7 including the stepsof:

extending an injection tubing string into the well bore;

connecting the injection tubing string in fluid communication with theproduction tubing string at a point adjacent the top of the subsurfaceearth formation; and

injecting a hot sulfur-solvent down the injection tubing string wherebythe hot sulfur-solvent mixes with the produced fluid in the productiontubing string and is produced up the production tubing string along withthe produced fluid to carry to the surface sulfur which may precipitatefrom the produced fluid in the production tubing string.

9. The method of claim 7 wherein the step of extending an insulatedtubing string into the annulus comprises extending concentric tubingstrings into the annulus and filling the annular space between theseconcentric strings with an insulating material.

10. A method for preventing sulfur deposition in the production tubingstring of a well producing a sulfurcontaining fluid from a subterraneanearth formation comprising the steps of;

flowing the sulfur-containing fluid from the production zone to thesurface through the production tubing string;

heating the outside of the production tubing string to heat thesulfur-containing fluid flowing through the production tubing string toretard sulfur deposition from the flowing fluid; and

injecting a hot sulfur-solvent into the flowing sulfurcontaining fluidthrough an injection tubing string at a point below a pack-off means insaid well. a:

3, 3? UNITED STATES PATENT QFFICE CERTIFICATE OF CORRECTION Patent No.3,796,265 Dated March 12 1974 I JAMES R. EICKMEIER It: is certified thaterror appears inthe above-identified patent and that said LettersPatentare hereby corrected as shown below:

r- The Patent should read:

"[30] Foreign Application Priority August 19, 1971, Canada 120,935"

Signed and sealed this 22nd day of October 1974.

Y SEAL) I Attest McCOY M. GIBSONIJR. C. MARSHALL DANN Attesting OfficerCommissioner of Patents

2. The method of claim 1 where the hot fluid is steam.
 3. The method ofclaim 1 where the heated fluid has a temperature sufficient to maintainthe temperature of the flowing sulfur-containing fluid above the meltingpoint of sulfur.
 4. The method of claim 1 including the step ofinjecting a hot sulfur-solvent into the flowing sulfur-containing fluidthrough an injection tubing string connected in fluid communication withthe production tubing string at a point below a pack-off means in thesaid well.
 5. The method of claim 4 where the hot sulfur-solvent is aheated light crude oil.
 6. The method of claim 4 wherein the hotsulfur-solvent is heated to a temperature in the range of 250* to 450*F.
 7. A method of producing a fluid having a high hydrogen sulfidecontent from a fluid-containing subsurface earth formation through wellswithout plugging the wells with sulfur precipitate which comprises thesteps of: providing a well bore extending from the earth surface to thesubsurface earth formation; lining at least a part of the well bore witha tubular casing; completing the well bore in fluid communication withthe subsurface earth formation; extending a production tubing stringinto the wellbore to a point adajacent the subsurface earth formationwhereby an annulus is defined between the tubular casing and theproduction string of tubing; packing off the annulus with a pack offmeans set at a point in the well bore above the subsurface earthformation to prevent fluid flow up the annulus from the subsurface earthformation; extending an insulated circulating tubing string into theannulus to a point above the pack off means; producing fluid having ahigh hydrogen sulfide content up the production tubing string from thesubsurface earth formation; and simultaneously circulating a hot fluiddown the insulated circulating string and up the annulus to heat theproduced fluid in the production tubing string and thereby retard sulfurprecipitation in the production tubing string
 8. The method of claim 7including the steps of: extending an injection tubing string into thewell bore; connecting the injection tubing stRing in fluid communicationwith the production tubing string at a point adjacent the top of thesubsurface earth formation; and injecting a hot sulfur-solvent down theinjection tubing string whereby the hot sulfur-solvent mixes with theproduced fluid in the production tubing string and is produced up theproduction tubing string along with the produced fluid to carry to thesurface sulfur which may precipitate from the produced fluid in theproduction tubing string.
 9. The method of claim 7 wherein the step ofextending an insulated tubing string into the annulus comprisesextending concentric tubing strings into the annulus and filling theannular space between these concentric strings with an insulatingmaterial.
 10. A method for preventing sulfur deposition in theproduction tubing string of a well producing a sulfur-containing fluidfrom a subterranean earth formation comprising the steps of; flowing thesulfur-containing fluid from the production zone to the surface throughthe production tubing string; heating the outside of the productiontubing string to heat the sulfur-containing fluid flowing through theproduction tubing string to retard sulfur deposition from the flowingfluid; and injecting a hot sulfur-solvent into the flowingsulfur-containing fluid through an injection tubing string at a pointbelow a pack-off means in said well.